1. Field of the Invention
The present invention relates to anti-friction linear motion bearings and, more particularly, to linear motion bearing assemblies containing a plurality of rolling elements in recirculating load and return tracks.
2. Description of the Prior Art
Linear motion bearing assemblies are well known in the art and are used extensively in a wide variety of machines, machine tools, transfer systems and other equipment where one part is to be moved longitudinally with respect to another. These assemblies may comprise an inverted substantially U-shaped bearing carriage mounted astride a modified Y-beam, I-beam or T-beam shaped rail. A plurality of pairs of load bearing and return tracks are provided in association with the carriage for a plurality of recirculating rolling elements, such as for example balls or rollers. These rolling elements travel alternately through load bearing tracks and return tracks to facilitate movement of the carriage along the rail with minimum friction.
End caps are usually located on both longitudinal ends of the carriage and may have turnarounds formed therein for transferring the recirculating rolling elements from load bearing tracks to return tracks. The turnarounds typically comprise a semi-toroidal shaped track connecting a load bearing track to a return track. At the center of the semi-toroid, an inner guide may be provided to smooth the movement of the rolling elements around the curved position from the load bearing track to the return track and to prevent the rolling elements from bunching up in the turns. These end caps are usually formed out of plastic material using molds which form the curved tracks of the turnaround integral with the end cap.
Bores or channels are typically cut or drilled into the carriage body to form the return tracks for the recirculating rolling elements. See, for example, U.S. Pat. No. 4,797,012. In some embodiments, the return tracks are formed by drilling or cutting bores or grooves conforming in size to the dimensions of the rolling elements directly into the bearing carriage within the depending legs of the U-shaped structure. See, for example, U.S. Pat. No. 4,932,067. This procedure is time consuming, requires special precision grinding and/or drilling instrumentation and greatly increases the expense involved in the manufacture and assembly of linear motion bearings. Also, where the rolling elements are of small diameter, extreme care must be taken to insure that the bores are accurate and properly aligned.
In order to avoid these drawbacks, other embodiments place the entire return track in separate structure which extends around the outside of the depending legs of the U-shaped structure. See, for example, U.S. Pat. Nos. 4,662,763 and 4,632,573. These embodiments, however, tend to decrease the rigidity of the bearing carriage or to expand the width of the carriage by the amount of space required for the outside return tracks.
Substantially all of the aforementioned embodiments require that a number of mounting holes be drilled into the carriage to insure proper alignment of the relatively large number of molded and machined parts to be assembled. All of these operations must be done with great precision in order to insure a dependable linear motion bearing assembly that can provide good service even under adverse operating conditions.
Other approaches have involved the reduction of both load bearing and return tracks into discrete elements including separate end caps, closure elements/intermediate members and/or side plates. See, for example, U.S. Pat. Nos. 4,869,600, 4,746,228, 4,674,893 and 4,637,739. These approaches necessarily require the intricate and accurate alignment and assembly of a number of separate elements as well as separate moldings for the individual elements.
Therefore, it would be highly desirable to have a dependable linear motion bearing assembly which avoids the need for extensive drilling and/or grinding of mounting holes and return tracks into the depending legs of the carriage and which is easily assembled utilizing a minimum number of molded parts without drilling mounting holes in the bearing carriage.
Accordingly, it is one object of the present invention to provide a linear motion bearing assembly wherein the return tracks are outside the depending legs of the carriage body.
It is a further object of the present invention to provide a linear motion bearing wherein the end caps and outer portions of the return tracks are integrally formed in an interfitting configuration thus eliminating the need for a large number of separate molded parts.
It is also an object of the present invention to provide a dependable linear motion bearing assembly which can be easily fabricated with a minimum number of molded parts without the need for mounting holes to be drilled into the carriage block.
These and other highly desirable objects are accomplished by the present invention in a linear motion bearing having return tracks outside the depending legs of the bearing carriage and wherein the end caps and portions of the return tracks are integrally formed in interfitting configuration to facilitate assembly to the bearing carriage without the need for mounting holes to be drilled therein.
Objects and advantages of the invention are set forth in part herein and in part will be obvious therefrom, or may be learned by practice with the invention, which is realized and attained by means of the instrumentalities and combinations pointed out in the appended claims. The invention consists of novel parts, constructions, arrangements, combinations, steps and improvements herein shown and described.